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Post by Fibonacci on Jul 29, 2023 15:53:04 GMT -8
Sure... It IS a pretty clever concept from the golden era when Britain was an innovation powerhouse (the Spitfire, Land Rovers, Mini, Jet engines etc). I imagine slide rules and Proper Yorkshire tea sipped out of chipped enamel mugs ![:)](//storage.proboards.com/forum/images/smiley/smiley.png) There are some deliberate design decisions inside the body such as the smooth dish shaped depression that makes me think the air bleed past the LP Tilt Valve stem was well accounted for. The inner surfaces leading to the intake horn have been smoothed and rounded like a gas-flowed cylinder head! Maybe they had some original Merlin V12 influence on their namesake? The clearance around the slot for the Tilt Valve stem is larger than it really needs to be, so its either for achieving the correct volume of air delivered to the case vs directed up the Venturi and/or to allow 1-2 degrees of rotation of the Venturi Tube and slightly adjust the distance to the LP Diaphragm rub plate? Merlin Venturi and LP Tilt Valve by fibonacci101, on Flickr Merlin Venturi and LP Tilt Valve detail by fibonacci101, on Flickr
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Post by vance on Jul 29, 2023 16:13:32 GMT -8
Thanks for the photo! It's lovely!
What a piece of engineering. A lot of DH regs could have benefitted from a venturi tube. Some did, but others missed the boat.
I agree, the width of the slot probably allows for a bit of fudging the lever height, and the air escaping from the slot into the box helps the diaphragm return to extension quickly. That was common practice.
BTW, I live near a small airport that hosts at least one WWII American Mustang fighter with the Merlin (Packard?) V12 engine. I hear it go over now and then, and it's sound is unmistakable. Well, it could be a P-40....
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Post by SeaRat on Jul 29, 2023 16:36:42 GMT -8
LP Venturi seat appears to be angled at 7 deg to allow the LP Tilt Valve correct interface to the LP Diaphragm. While most of the air will go straight up the venturi tube, a significant amount will vent past the Tilt Valve stem into the can... swirl around and then go up the inhale hose. Wonder how they worked that percentage out?! Merlin LP Tilt Valve and Venturi Tube ASSY by Graeme Cameron, on Flickr Very interesting design. Many tilt valve stems reach the diaphragm via a bend in the rod. It seems it would have worked in this case. The venturi tube slot would work as a guide to keep the valve from rotating. Is there some airflow advantage in their method? You might get away with slightly rotating the venturi tube to adjust lever height, but turning it off-center might cause the stem to bind in the slot. Okay, I'm now curious; where is the spring that holds the tilt valve in place? Usually there is a spring who's purpose is to hold the seating surface right next to the actual seat, but I don't see anything here. Are they simply assuming air pressure will keep the seat against the sealing surface? John
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Post by Fibonacci on Jul 29, 2023 16:56:27 GMT -8
Nope... no spring in this design! The spherical end of the LP Tilt Valve fits closely into a corresponding spherical recess in the body. The square edged recess is for a sealing washer to the Venturi Tube. So yes air pressure holds it up in place, I imagine the reg would hiss for a second or two when first pressurised? When depressurised it drops back slightly from the 7 deg seat in the Venturi Tube. So also has the benefit of no excessive engraving of the LP seat over time... Merlin Venturi LP Tilt Valve pivot detail by fibonacci101, on Flickr
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Post by vance on Jul 30, 2023 7:21:25 GMT -8
I really like the elegance of this design, even though it violates the KISS principle. In contrast, the Sportsways DualAir has an immense jet drilled into the tilt valve guide which is positioned close to, and pointed right down the intake horn rather than the complex venturi tube. The Sportsways valve stem is bent, and the bend can be adjusted to get the proper height. Note the slot/guide. ![](https://i.imgur.com/r4q0RcM.jpg) ![](https://i.imgur.com/8yOCZvk.jpg)
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Post by Fibonacci on Jul 30, 2023 14:45:33 GMT -8
Interesting, thanks for posting… hadn’t seen the insides of a Sportsways DualAir before! Note the much narrower slot where the tilt valve stem moves. So how does it breathe compared to say a RAM?
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Post by vance on Jul 30, 2023 15:13:23 GMT -8
I have had a couple of DualAirs, but only tried them out in a pool. They breathe very well.
I'm not a big fan of tilt valve regs. It's just personal preference (and prejudice). I prefer the HydroTwin and the HTII with their more complex, but IMO better second stages to the DualAir.
Your Merlin ought to be a good performer.
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Post by SeaRat on Jul 30, 2023 20:31:19 GMT -8
I have had a couple of DualAirs, but only tried them out in a pool. They breathe very well. I'm not a big fan of tilt valve regs. It's just personal preference (and prejudice). I prefer the HydroTwin and the HTII with their more complex, but IMO better second stages to the DualAir. Your Merlin ought to be a good performer. I think the problems with the tilt valve were identified by Dick Anderson of Healthways when he did tests against the USD Calypso, and found the tilt valve wanting big time at 200 feet. He said something like it was like sucking air through a straw. Healthways then started testing a downstream second stage that could be built on their tilt valve second stage bodies. He finally got close to Calypso performance with a downstream second stage with a hole pointed at the mouthpiece. So that’s what Healthways ran with. I think the tilt valve has a real problem allowing enough dense air through the restricted orifice that is the tilt valve at depth. John
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cg43
Pro Diver
![*](//storage.proboards.com/forum/images/stars/star.png) ![*](//storage.proboards.com/forum/images/stars/star.png)
Posts: 109
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Post by cg43 on Jul 31, 2023 14:47:03 GMT -8
Hello
An downstream valve is easy to compensate for cracking suction by the force off the spring , and during highter flöwrate with ventury . The doubelhose with it's big area diaphragm has the nessesary torque to open an tilt valve that's give you all the air you need . A singelhose with tilt valve and an small diaphragm can breath easy (low cracking suction) or give plenty of air , but you cannot have both . A long stem , a tiny orivice and low IP make breath (during low flowrate) easy but give less air . As long as you breath in the limits of the tiltvalve it's easy . Diver who never reach the limit are happy with this valves.
Greetings Rainer
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